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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Chaetostichium (Hochst.) C.E. Hubb.

~ Oropetium

Habit, vegetative morphology. Perennial; densely caespitose. Culms 5–12 cm high; herbaceous. Young shoots intravaginal. Leaves not basally aggregated. Leaf blades narrow; 0.3–1.2 mm wide (1–5 cm long); subsetaceous, rigid, flat or convolute; exhibiting multicellular glands abaxially. The abaxial leaf blade glands intercostal. Leaf blades not pseudopetiolate; without cross venation; disarticulating from the sheaths (apparently). Ligule a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence a single spike (slender, becoming recurved, to 8 cm long). Rachides hollowed (excavated to receive the spikelets). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate (the ranks adjacent); sessile.

Female-fertile spikelets. Spikelets 3–5 mm long; adaxial; compressed dorsiventrally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (minute, shortly bearded). Callus short.

Glumes one per spikelet, or two; (G2) relatively large; when two, very unequal; (G2) long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; (the upper) awned (attenuate into a straight or curved awn to 7 mm long); non-carinate; very dissimilar (G1 hyaline, tiny or missing, G2 linear-lanceolate, acuminate, awned, leathery). Lower glume 0 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1. Lemmas emarginate; less firm than the glumes (membranous); not becoming indurated; not deeply cleft; mucronate, or awned (minutely). Awns when present, 1; median; non-geniculate; much shorter than the body of the lemma; entered by one vein. Lemmas hairless; non-carinate; 3 nerved. Palea present; relatively long (slightly shorter than lemma); apically notched (emarginate); with apical setae (via excurrent nerves); not indurated (membranous); 2-nerved; 2-keeled. Lodicules present; 2; free; glabrous. Stamens 3. Anthers 0.6–1 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea (included); small (2.5 mm long); fusiform; compressed laterally. Hilum short. Pericarp loosely adherent (removable when soaked). Embryo small (about 1/4 the length of the fruit).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (medium-thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 12 microns long. Microhair total length/width at septum 1.5. Microhair apical cell/total length ratio 0.3. Stomata common. Subsidiaries dome-shaped. Guard-cells overlapping to flush with the interstomatals (but the subsidiaries overlapped by the adjoining intercostals). Intercostal short-cells absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; exclusively saddle shaped (a rather angular version of this type).

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma; not traversed by colourless columns (but almost so). Midrib conspicuous (by virtue of a large, round abaxial keel, with a large anchor of sclerenchyma); with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (all the primaries with big anchors). Sclerenchyma all associated with vascular bundles (but the smaller bundles having their abaxial sclerenchyma in lateral groups, rather than directly opposite).

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae (as a synonym); Cynodonteae; Tripogoninae. 1 species (C. minumum).

Distribution, phytogeography, ecology. Montane Northeast Africa.

References, etc. Morphological/taxonomic: Hubbard 1937b. Leaf anatomical: studied by us.

Illustrations. • C. minimum (as C. majusculum): Jacques-Félix, 1962

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.